The delivery of bioactive components (proteins, lipids or hydrolysates thereof, and probiotic microorganisms, for example) in food or other ingestible products is constrained by the need to provide a safe product with a useful shelf life while retaining bioactivity. Products with a useful shelf life are said to have a good keeping quality and are less prone to spoilage.
Delivery of bioactive components is desirable at least because such components are physiologically active when ingested and can have positive health benefits, including but not limited to bone health, immune benefits, anti-inflammatory activity, heart health and efficacy in cancer treatment.
Traditional means of ensuring a useful keeping quality have a negative impact on the bioactivity of food products and the like. In particular, thermal processing is not generally suitable for the production of commercially sterile bioactive products. For example, an analysis of immunoglobulin proteins in commercial dairy products revealed that although between 60% and 75% of the immunoglobulins are retained through pasteurisation, levels in UHT or canned (evaporated) milk are negligible (Li-Chan et al, 1995). Commercial sterility in acid foods may be achieved by employing a lower-temperature heating than that used in canning, but the sensitivity of immunoglobulins to denaturing under heating is exacerbated by acidification (Dominguez et al, 2001).
A probiotic microorganism is one that when administered in an adequate amount confers a health benefit on the host. While the live probiotic microorganism exhibits a bioactive effect, an inactivated probiotic microorganism may provide the bioactivity in a stable, less technically restricted format for use and distribution. In applications where it is undesirable to have live microorganisms because of their unwanted activities (such as enzyme or acid secretion, for example), inactivated microorganisms may be advantageous in still providing the bioactivity, without the unwanted activity resulting from their viability. International PCT application WO 20041032655 reports use of high pressure treatment to reduce microbial spoilage in foods and/or to render the food safe for consumption, while retaining viable desired cultures.
There are many processes in the manufacture of bioactive products, ingredients and foods that may result in a partial or complete loss of bioactivity. In the case of dairy-based ingredients and foods, processes that involve heating steps that may affect bioactivity include thermal pasteurisation, homogenisation, thermalisation, evaporation and drying. In the case of food processing, examples of heating steps that may affect bioactivity include heat treatments preceding fermentation, UHT-treatments, retorting, hot filling and hot packing. A bioactive component will typically be subjected to one or more of these heating steps during the manufacture of a food. This is particularly true of dairy-based products where processing always includes an initial pasteurisation step and typically includes further heating steps prior to packaging and sale. Korhonen et al (1998) report that heating to temperatures in the range 60° C. to 90° C. denatures proteins therefore reducing the activity of bioactive proteins.
Drying of products produced using pasteurised milk may be used to improve keeping quality with losses of up to 40% of immunoglobulins (Li-Chan, 1995), but commercial applications are then limited to direct consumption (for example, tablets) or fresh products (for example, yogurt) where the dried bioactive ingredient is not subsequently heated again. Losses due to drying and heating may be compensated for by supplementing intermediate or final products with the bioactive component of interest but this can increase the cost to the end consumer.
Pressure treatment with pressures above about 350 MPa has been reported to achieve commercially-useful improvements in keeping quality for meat, vegetable and fruit-based products (such as cooked ham, avocado products and juices respectively). However, Huppertz et al (2002) report that high pressure denatures whey proteins in milk. Additionally, Korhonen et al (1998) report that pressure treatments at pressures of about 500 MPa and above irreversibly denature proteins in most cases. Felipe et al (1997) report that appreciable levels of immunoglobulin denaturation occur in goat's milk at pressures of 500 MPa.
Masuda et al (2000) report that pressures of 400 MPa and above may not be used to improve the keeping quality of bovine colostrum because such pressures denature the immunoglobulin protein.
Tonello et al (1992) report that pressures of 200 MPa applied for 2 hours may be used to retain at least 85% of the immunoglobulin activity, although the microbial load of colostrum is reduced by less than 2-log cycles. The same process at 63° C. can reduce the microbial load below limits of detection (more than 7-log cycles), but at least 50% of the immunoglobulin activity is lost.
The need exists for a process that can provide a commercially useful keeping quality for a bioactive product such as a food or other ingestible product while retaining the bioactivity of at least one bioactive component.
Therefore it is an object of this invention to provide an improved or alternative method of preventing the growth of unwanted microorganisms while retaining at least a desired level of activity of at least one bioactive component or to at least provide the public with a useful choice.